Alarm device



Filed July 28. 1930 Vania/a;

'j 4 i 2 JJ INVENTOR MAXIMHJMN .IULIJS OTTO SYRUTT ATl'ORN EY Patented Apr. .28, 1936 ALARM DIIVIGEl Julius Otto Strutt, lEindhoven,

Netherlands, assigner to Radio Corporation of America, a corporation of Delaware Application July 28, 1930, Serial No. 471,214

the Netherlands July 21, 1929 4 claims. (ci. 1v1-314i l This invention relates to an alarm device for safeguarding ,rooms and other spaces and is based on the discovery that the reception-intensity ol an ultra-short wave receiver is greatly inuenccd.

the conditions controlling the distribution of the ileld become varied and the result will be that quite a different field distribution is established. The body of the person that enters may in some 55 measure be looked upon as a secondary trans mitter which transmits part of energy retained and thus alters the eld distribution.

Evidently, the larger-the size of the extraneous body and of the room in relation to the wave 5 by variations occurring in the vicinity of a translength, the greater is the variation in the eld 5 mitter and a receiver. 'Ihe vicinity of the transdistribution. It has thus been found that an esmitter and the receiver is to be understood heresential condition of securing a powerful influence lnaiter to mean the surroundings of about ten on the reception-intensity consists in that the l wave lengths. size of the room in which the transmitter and the On the transmitter and the receiver being arreceiver are arranged should be large in relation 10 ranged in a room or other space, a deiinite oscilto the wave length. The invention will be more latory condition arises, said condition being conclearly understood by reference to the accomtrolled by the surroundings of the transmitter panying drawing in which a diagrammatic survey and the receiver. is given of, the arrangement of the component l5 It in such a space a variation in condition ocmembers of an alarm device according to the in- 15 curs, Tor example ii any one enters the room, -the vention. y prevailing oscillatory condition will become va- Referring to the gure, i designates a transried, and the reception intensity is thus at once mitter, 2 a receiver and 3 an alarm signal which affected. This phenomenon is not limited by 8f becomes operative when variations occur Within 2o closed chamber but also occurs in the open as the room in which the transmitter and receiver 20 long as there is in the vicinity of the transmitter are arranged. or receiver some object that can serve as a re- The transmitter and receiver are preferably iiector. furnished with a triode to which a Lecher sys- Thus, for example,a bush or shrubbery may tem is connected. The arrangement of the transsuiiice to bring about a considerable variation mitter and the receiver per se is no important 25 in the reception-intensity. v feature o the invention but it is essential that It has been found that when the hand is apthey shouldl be arranged for very short waves, preached to a short-wave -transmitter or receiver, say of the order of a meter. 'if the tuning and consequently e150 the reception- For suitable receiving and transmitting appaintensity varies. This principle can be, applied ratus for accomplishing the purposes of this in- 3o 7 to alarm signals and the variation in the recepvention attention is invited to the article in the e tion-intensity can be rendered perceptible in a Proc. I. R. E., June 1928, page '715 by Yagi, en-

suitable manner at a distant point. However, titled Beam transmission of ultra-short waves. these capacitative influences only occur when the The output circuit of the receiver is connected 35 variation takes place in the immediate vicinity of to a conductor 4 which leads to the alarm device the transmitter or receiver. 3 proper. The receiver includes a detector which The alarm device according to the invention is converts high frequency oscillations into direct based on another phenomenon which has the current or into low frequency oscillations which o great advantage 'of not being dependent upon a can be transmitted through the conductor i to a o small spacing between the transmitter or redistant point. Ii for the supply of the vplate of ceiver and the object or body that induces the the transmitter an alternating Current is used a variation in the tuning. wave modulated in amplitude is emitted which It may be imagined that in an enclosure conafter rectification by the receiver supplies an altaining the transmitter stationary waves are proternating current which can be easily transmitted' .g5 duced by reason of reflection on the walls, the to the alarm device. door and the ceiling, the distribution and the ar- The alarm device may be made in diderent rangement of the nodes and loops of said waves ways. The construction of the alarm device per being inuenced inter aha by the objects enclosed se does not fall within the scope of the invention. within the room. If anyone enters the enclosure, It may, for example, consist of an alternating cur- 5@ rent relay the armature of which as soon as it drops by reason of the variation in current strength in the relay winding closes a circuit of an acoustic or optical signal. As an alternative,

it is, of course, possible to operateentirelyuwith 5s direct current. Preference is given to a closed in and causing a perceptible change in the intencircuit relay.

If necessary, the currents received may be amplied subsequent or prior to detection.

Preferably, the receiver is arranged at a point where the reception-intensity is maximum.

I claim: v

1. In an alarm device for indicating the presence oi an extranwus body within an enclosure' a source of radiant energy within the enclosure for permeating the enclosure with energy having a wave length which is small compared to the size ci the enclosure, a radiant energy intercepting device in the enclosure positioned therein so as to be affected by energy impinging thereon directly from the source as well as indirectly as from energy from the source as reiiected from the walls of the enclosure and objects therein and indicating means associated with the intercepting den vice for indicating changes in the intensity of the energy received by the intercepting device as caused by the presence of an extraneous body' within the enclosure.

2. In an alarm system the steps in a method of producing indications of the presence oi extraneous bodies within an enclosure which comprise permeating the space within the enclosure with radiant energy waves having a wave length which is small compared with the dimensions oi the enclosure, normally producing from the radiant energy within the enclosure responses of predetermined intensity characteristics dependent upon the interception of the radiant energy at a point within the enclosure, both directly from the source and from reiiections of the energy from the walls of the enclosure and objects theresity response characteristics by the reflection and absorption characteristics oi any extraneous body present .within the enclosure to thereby indicate immediately the presence oi the extraneous body therein.

3. The method of detecting the introduction of a new object into a given substantially enclosed space and the disturbance o! objects therein, whichconsists in propagating in said space continouous waves oi' a wavelength substantially greater than that of light, which waves are reflected by the coniines of said space and by objects therein to produce reiiected waves, and which reflected waves form with each other and with said propagated waves a wave pattern s'ubstantially filling said space; in receiving the waves comprised in said pattern at a xed region within said space; and in signallingy variations in the amplitude of said'received waves, whereby to detect changes in said pattern.

4. 'I'he method oi' detecting the introduction of an object into a given substantially enclosed space and the disturbances of objects therein, which method includes the steps of propagating in said space continuous energy waves, which waves are reflected by the coniines of said space and by objects therein to produce reilected waves, and which reilected waves form with each other and with the propagated waves a pattern substantially lling the space; receiving the waves comprised in said pattern at a fixed region within said space; and signalling variations in amplitude ci the received waves whereby to detect changes in said pattern.

` MAXIMJLLAAN JULIUS OTTO B'I'RUTI. 

